Blasting explosive cartridge and borehole charge



2 Sheets-Sheet 1 INVENTQRS,l Whia ATTORNEY.

AU: EPT [2| P' @Villa Filed July 24, 1 9'34 f A. G. WHITE ET AL .AprI 6, 1937.

' BLSTING EXPLOS/IVE CARTRI'DGE AND BOREHOLE CHARGE FIG.. 1.

M a e FIG. 2.

April 6, 1937. A. G. WHITE ET AL 2,075,969

BLASTING EXPLOSIVE CARTRIDGE AND BOREHOLE CHARGE,

Filed July 24, 1954 2 Sheets-Sheet 2 FIG. 5.

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Patented Apr. 6, 1937 Y UNITED STATES PATENT OFFICE BLASTING EXPLOSIVE CARTRIDGE AND BOREHOLE CHARGE Application July `24, 1934, Serial No. 736,752 In Great Britain July 24, 1933 7 Claims.

'Ihis invention relates to blasting explosive cartridges and borehole charges of the type in which a core of explosive is provided with a jacket of one or more cooling substances capable of cooling 5 or blanketing the hot products of combustion, either by evolving non-infiammable gases and/ or by decomposition or change of state with corresariding absorption of heat.

e principal object of the invention is to prol de a blastingexplosive cartridge or borehole charge comprising gunpowder or similar slowburning explosive, which is made sufficiently safe for use in fiery mines. The chief advantage of gunpowder when used as a blasting explosive is l that its action is less drastic and localized than that of detonating explosives such as nitroglycerine, and accordingly a higher proportion of lump material with less slack is obtained as a result of the blast.

Gunpowder however gives a flame which is very apt to ignite redamp or coal dust and it is therefore too dangerous for use in fiery mines. The introduction of cooling salts into gunpowder has not up to the present been successful, since it is found that the quantity of cooling salts which would be necessary to render gunpowder safe for use in ery mines frequently results in failure of propagation of the explosion under normal conditions.

We have also found that the cooling substance hitherto found eective as sheathing materials for detonating explosive cartridges of the nitroglycerine type are of relatively little value when l used to sheath a charge of gunpowder or similar explosive.

The present invention is based on the discovery that, by surrounding an explosive charge consisting essentially of gunpowder or the like with a jacket comprising a borate, preferably borax,

with or without boric acid, blasting cartridges or borehole charges are produced which are characterized by a high degree of safety'combined with a sufciently rapid rate of burning. The addition of boric acid is mainly for the purpose of improving -the mechanical properties of the sheathing material. In addition to borates', the jacket may contain small proportions of inert materials or of other salts commonly employed as cooling agents `for blasting explosives, with or without small amounts of binding or waterproofing agents. As cooling agents there may be mentioned alkali metal chlorides, in particular sodium or potassium chloride, or ammonium oxalate or bicarbonate or alkali metal oxalates or bicarbonates. The explosive charge forming the core of the cartridge may also contain a small quantity of one or more solid cooling salts such as mentioned above and/or a small quantity of boric acid or borates.

By applying the borate together with anyother solid cooling salts, if such are employed, in the form of a jacket or sheath, the proportion of cooling substance in the cartridge or borehole charge ot burning explosive as a whole may be raised considerably above that hitherto found practicable and without materially reducing the rate of burning or power of the explosive. Preferably, the jacket extends over the entire length of the core of explosive, and each or either end of the core is also covered by a plug or disc of the sheathing material, or of other suitable inert material or cooling substance. The plugs or discs may be provided with a channel for the introduction of an igniter.

The charge of explosive may be in granular form, or in the form of a compressed pellet which may have a longitudinal channel for the introduction of an igniter, or an inner core of explosive of sensitiveness and rate of burning relatively higher than the remainder of the explosive charge.

'I'he jacketing material may be applied to the explosive charge' in several ways. For example, it may be cast or pressed into the form of a tube or cup into which the charge of gunpowder may be introduced either loose or in the form of a compressed pellet. In this case the cartridge may be held together by a wrapping of waxed or unwaxed paper or the like. Alternatively, the charge of gunpowder may be introduced into the central space of a double-walled annulus of paper or the like containing loose jacketing material.

If desired, the jacketing material and gunpowder-may be suitably arranged in a. container, preferably of'` metal such as tinned iron sheet, which is loaded into the borehole, or the gunpowder may be placed in the borehole in the form of a lpellet and the jacketing material placed around it. The jacketing material may also be formed aroun'd a pellet by pressure in a suitable mould, or the granular explosive and jacketing material. may be placed in the desired relative positions in a mould and pressed into shape simultaneously. The two last mentioned methods have the advantage that the cooling material is firmly adherent to the explosive core and cannot readily be separated from it.

` If desired, both the explosive core and the completed cartridge may be wrapped in paper or similar material.

The requisite thickness of the sheath will depend to some extent'upon its composition, but in most cases we ilnd that a thickness of 4 mm. is sucient to render the cartridge safe for use in fiery and dusty mines. l

The invention will now be further described with reference to the accompanying drawings in l0 which Figure 1 is a sectional elevation of an apparatus suitable ior producing a sheathed cartridge of gunpowder or the like as an integral unit.

Figure 2 is a plan view oi the apparatus illustrated in Figure 1.

. Figures 3 to 6 are diagrammatic representations of a sheathed cartridge produced in accordance with the invention and provided with a longitudinal channel for the insertion of an4 an annular piston C to t inside the cylinder A and over the pin B, and a thin sheet metal cylinderV E, which is used as a temporary separator between the blackpowder charge and the sheathing material. All the components are preferably made of non-ferrous metal.

The operation of making a pressed sheathed pellet is carried out as follows. The cylinder A is placed in position on the base D and the pin B is inserted in position. 'Ihe thin walled cylinder E, which is preferably provided with lateral prongs or the like to ensure its central position in the device, is placed as shown in the diagram. A suitable charge of blackpowder for a single pellet is poured into the space formed between 40 the annular cylinder E and the pin B, and powdered borax is poured into the annular space between the annular cylinder E and Vthe outside cylinder A until the levels of the'powders inside and outside the cylinder E are equal. Alternatively, a previously formed pellet of blackpowder and of suitable dimensions may be inserted within the cylinder E. Cylinder E is then withdrawn with as little disturbance of the charge as possible, and the annular piston C is placed over the pin B so that it rests lon the powder in the mould The whole assembly is then transferred to a suitable press and subjected to a heavy pressure until the materials are thoroughly compacted together. A pressure of 2 tons weight for 2 minutes is usually sumcient to produce a very compact pellet which can be handled without risk of damage., After the lpressure is released the assembly is taken apart by removing the` base D and pressing out the central pin B which carries the compressed pellet with it. The pellet is then easily withdrawn from the pin. When it is desired to produce pellets without a hollow core, the central pin.B is replaced by a 6 ilat circular disc. Automatic weighing and charging devices may be employed to supply the blackpowder and sheathing materials respectively to the mold. -I The proportion of sheathing material to explosive core is conveniently regulated by selecting an annular separatingv cylinder of appropriate diameter. v

` The materials may be used dry, or containing up to 5% moisture. Pellets which have been pressed from blackpowder containing appreciable quantities of moisture are caused to set hard by drying them after the pressing operation.

'I'he present invention is particularly applicable to the production of safety explosive cartridges comprising gunpowder as the explosive ingredient, for example a gunpowder consisting of approximately 75%-potassium nitrate, 15% charcoal and 10% sulphur. The proportion of these ingredients may, of course, be varied as is known in the art. The invention is, however, also applicable to the sheathing, for safety purposes, of other slow burning explosives having properties resembling gunpowder, By the term slow burning explosives, as used in this specification and in the appended claims, we mean an explosive `composition falling within Class 1 or 2 of the British Home Otllce List of Authorized Explosives.` That is to say, the invention includes within its scope explosive compositions consisting of a mechanical mixture of a -nitrate or a perchlorate with carbon or any other non-explosive carbonaceous material with orwithout other combustible materials such as sulphur. Thus, for example, the invention includes sheathing with a borate explosive material such as sodium nitrate gunpowder, e. g. 73% sodium nitrate, 17% charcoal and A10% sulphur, or a composition consisting of 44% sodium nitrate, 34% ammonium perchlorate and 22% charcoal.

The sheathing material which is preferred for use in accordance with the present invention is sodium borate with or without an admixture oi.' borlc acid, but other borates may also be used, for example barium borate, zinc borate, magnesium borate, manganese borate and ammonium borate.

Example 1 A cylinder of thin sheet -metal having an internal diameter of 1% inches is arranged to stand concentrically in a vertical cylindrical mould ot internal diameter 11"; inches, which' is furnished with a central pin M1" in diameter. 2 ozs. of gun- A Example 2 2 ozs. of gunpowder are loaded into the central space of the mould used in Example 1, on top oi. a layer of borax containing 30% borlc acid, and the annular space is then iilled as before with a mixture of powdered borax containing 30% borlc acid. The partition is then withdrawn and the pressing operation carried out as before.

Example 3 2 ozs. of glmpowder are loaded into the central space of the press used in Example 1 on top of a layer of manganese borate, and the annular space is then filled with manganese borate. The total weight o1 manganese borate used is 2 ozs. The partition is then withdrawn and the pressing operationk carried out as before.

Example 4 2 ozs. of a mixture of 1 part by weight of potassium chloride with 2 parts by weight 0I Empowder are loaded into the central space ofthe press l used in Example4 1 on top of a layer of borax. The annularspace is filled with borax to the level of the gunpowder mixture. The separator is then withdrawn and a layer of borax is added to cover the gunpowder. The pressing operation is then carried out as before. The total quantity of borax used is V2 oz.

We claim:

1. A safety explosive cartridge or borehole charge comprising a. core of black powder and a sheath comprising a borate.

2. A safety explosive cartridge or borehole charge comprising a core of black powder and a sheath comprising borax.

3. A safety explosive cartridge or `borehole charge comprising a central core consisting of a compressed pellet of black powder and a sheath comprising a borate.

20 4. A safety explosive cartridge or borehole charge comprising a central core of black powder provided with a longitudinal channel'adapted to accommodate an igniter and a, sheath for the said core comprising a borate.

5. A method of forming a safety explosive cartridge which includes the step of feeding a sheathv l ing material into an annular space around a quantity of slow burning explosive and compressing the explosive and the sheathing material to form an integral unit.

6. A method of forming a safety explosive cartridge which includes the step of feeding a sheathing material into an annular space around an already formed pellet of slow burning explosive and compressing the explosive and the sheathing material to form an integral unit.

'1. A method of forming a safety explosive cartridge which includes the steps of feeding a sheathing material into an annular space around a quantity of slow burning explosive, compressing the explosive and the sheathing material to form an integral unit and dryingvthe compressed unit to form a hard compact mass.

ALBERT GREVILLE WHITE. ELWYN JONES. 

